The present invention relates to small sailing crafts in general and concerns a coupling element of the boom to the mast. Generally, the boom of small sailing crafts, and surf boards in particular, consists of two side-by-side tubes connected at their ends. The sail is inserted between the tubes and is fixed to the two ends of the mast and to one end of the boom. The other end of the boom has a coupling element to the mast and is maintained in the desired position by a binding. In particular, the boom can simply bear against the mast, being forced by the tension of the sail, or it can house the mast between the two tubes and be kept in contact with the coupling element by means of the said binding.
The the first case, the coupling element presents a fork on its outer edge adapted to house the mast, while in the second case the mast is housed in a cavity on the inner edge of the coupling element. In both cases, the area of contact between the coupling element and the mast consists of a concave cylindrical seating with should fit the mast perfectly and provide a large area of contact between the mast itself and the coupling element.
In reality, given that the position of the boom varies with the height of the user, the boom is not always perpendicular to the mast; in other cases, as the diameter of the mast is not standardized, it may happen that the mast does not enter the recessed area of the coupling element or there may be an excessive play between the mast itself and the seat.
In the first case, the contact between the mast itself and the boom is concentrated on a point with consequent rapid deterioration of the outer surface of the mast, while in the second case, the coupling of the mast and boom is unstable and the latter may tend to oscillate round its axis.
As stated above, the boom is fixed to the mast by means of a length of cord which is first wound round the mast and then fastened to the coupling element. The binding of the boom to the mast is generally effected placing the boom parallel to the mast, given that the coupling element is so shaped as to bring the binding into tension when the boom is brought into the working position. This movement of the boom, necessary to bring the binding into tension, is balanced by the friction forces generated by the movement of the coupling element on the surface of the mast.